The present invention relates to a new and improved construction of rapid change device for seives for straining or filtering plastic materials, such as typically, for instance, rubber, plastics and so forth.
During the extrusion of certain sectional shapes or hoses, particularly when fabricating pneumatic hoses for automobile tires, it is necessary that the plastic mass, which in the case of pneumatic hoses for vehicles or automobile tires consists of butyl rubber, be cleaned of foreign bodies or contaminants before it is further delivered for final fabrication or processing.
Both in this case, and also during the fabrication of sectional shapes, where there must be used filtered mixtures, in other words quite pure mixtures, it is generally a widely adopted procedure throughout the world that the unvulcanized mixture, following the mixing operation, is transported during a separate working step through a so-called strainer, i.e. a large extruder having filter sieves. The contaminants, which, on the one hand, are attributable to the raw materials which are used, and, on the other hand, also can be formed during the fabrication operation and during handling of the mixture while it is being processed until the final mixing thereof, are entrapped during this straining or filtering process. Hence, a clean mixture effluxes out of the strainer.
Depending upon the degree of the contaminants in the mixture, the sieves must sometimes be exchanged within relatively short time spans, for instance every ten minutes. When working with a strainer, where this filtering operation is carried out in separate working steps, one technique which has been employed in order to save time is to work with two injection or spraying heads. If the sieves or filters, which filter the mixtures, are clogged and must be exchanged, then the machine is stopped, the ejection head is dismantled from the extruder machine and rocked or pivoted out by means of a hinge arrangement. Then the second injection head with new sieves is again pivoted-in by means of a hinge arrangement mounted at the other side and fixed in place. Now the extrusion operation can be restarted. During the straining of the mixture or processed material at the second injection head the first injection head is cleaned and loaded with new, clean mesh sieves, typically wire sieves or filters.
This separate straining operation requires a separate work process during which, when working in shifts at the plant, it is necessary to employ for each shift at least two operators. Additionally, the cleaning of the entire first injection head and ultimately thereafter the second injection head requires a large expenditure in work on the part of the plant personnel. Also, this cleaning operation results in a corresponding loss of a certain amount of the mixture material. Just as was heretofore the case, even with this technique there exists, however, the danger of a renewed contamination of the mixture during handling, since the effluxing material "spaghettis" do constitute a semi-finished product which thereafter must be processed at the rolling mill or the like, in order to be finally delivered to the extruder fabricating the final product, whether it be hoses or sectional shapes or the like.